After defer the execution of clockgating enabling, at that time, gfx already
enter into "off" state. Howerver, clockgating enabling will use MMIO to access
the gfx registers, then get the gfx hung.

So here we should move the gfx powergating and gfxoff enabling behavior at the
end of initialization behind clockgating.
Signed-off-by: NHuang Rui <ray.huang@amd.com>
Reviewed-by: NHawking Zhang <Hawking.Zhang@amd.com>
Acked-by: NChristian König <christian.koenig@amd.com>
Cc: Felix Kuehling <Felix.Kuehling@amd.com>
Signed-off-by: NAlex Deucher <alexander.deucher@amd.com>